The miniaturization of semiconductor circuit elements has reached a point where feature sizes of 32 nm, 28 nm, and even 22 nm are fabricated on a commercial scale. As the dimensions continue to get smaller, new challenges arise for seemingly mundane process steps like filling a gap between circuit elements with a dielectric material that acts as electrical insulation. As the width between the elements continues to shrink, the gap between them often gets taller and narrower, making the gap difficult to fill without the dielectric material getting stuck to create voids and weak seams. Conventional chemical vapor deposition (CVD) techniques often experience an overgrowth of material at the top of the gap before it has been completely filled. This can create a void or seam in the gap where the depositing dielectric material has been prematurely cut off by the overgrowth; a problem sometimes referred to as breadloafing.
One solution to the breadloafing problem has been to use liquid precursors for the dielectric starting materials that more easily pour into the gaps like filling a glass with water. A technique currently in commercial use for doing this is called spin-on-glass (SOG) and takes a liquid precursor, usually an organo-silicon compound, and spin coats it on the surface of a substrate wafer. While the liquid precursor has fewer breadloafing problems, other problems arise when the precursor material is converted to the dielectric material. These conversions often involve exposing the deposited precursor to conditions that split and drive out the carbon groups in the material, typically by reacting the carbon groups with oxygen to create carbon monoxide and dioxide gas that escapes from the gap. These escaping gases can leave behind pores and bubbles in the dielectric material similar to the holes left behind in baked bread from the escaping carbon dioxide. The increased porosity left in the final dielectric material can have the same deleterious effects as the voids and weak seams created by conventional CVD techniques.
More recently, techniques have been developed that impart flowable characteristics to dielectric materials deposited by CVD. These techniques can deposit flowable precursors to fill a tall, narrow gap without creating voids or weak seams, while avoiding the need to outgas significant amounts of carbon dioxide, water, and other species that leave behind pores and bubbles. Exemplary flowable CVD techniques have used carbon-free silicon precursors that require very little carbon removal after the precursors have been deposited in the gap.
While the new flowable CVD techniques represent a significant breakthrough in filling tall, narrow (i.e., high-aspect ratio) gaps with dielectric materials such as silicon oxide, there is still a need for techniques that can seamlessly fill such gaps with carbon-rich, low-κ dielectric materials. These materials generally have a lower dielectric constant (κ) than a pure silicon oxide or nitride, and typically achieve those lower κ levels by combining silicon with carbon species. Among other topics, the present application addresses this need by describing flowable CVD techniques for forming silicon-and-carbon containing dielectric materials on a substrate.